Store and read hash and array in files in Perl

Question

I\'m a noob.I need some basic knowledge about how data should be saved and read under perl. Say to save a hash and an array. What format (extension) of file should be used?

Answer 1

If you new I just suggest make to string from array/hash with join() and they write it with "print" and then read and use split() to make array/hash again. That would be more simple way like Perl teaching text book example.

Answer 2

Perlmonks has two good discussions on serialization.

• How to save and reload my hash
• How can I visualize my complex data structure?

Answer 3

This really depends upon how you'd like store your data in your file. I will try writing some basic perl code to enable you to read a file into an array and or write back a hash into a file.

#Load a file into a hash.
#My Text file has the following format.
#field1=value1
#field2=value2  
#<FILE1> is an opens a sample txt file in read-only mode.
my %hash;
while (<FILE1>)
{
  chomp;
  my ($key, $val) = split /=/;
  $hash{$key} .= exists $hash{$key} ? ",$val" : $val;
}

Answer 4

You're looking for data serialisation. Popular choices that are robust are Sereal, JSON::XS and YAML::XS. Lesser known formats are: ASN.1, Avro, BERT, BSON, CBOR, JSYNC, MessagePack, Protocol Buffers, Thrift.

Other often mentioned choices are Storable and Data::Dumper (or similar)/eval, but I cannot recommend them because Storable's format is Perl version dependent, and eval is unsafe because it executes arbitrary code. As of 2012, the parsing counter-part Data::Undump has not progressed very far yet. I also cannot recommend using XML because it does not map Perl data types well, and there exists multiple competing/incompatible schemas how to translate between XML and data.

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Code examples (tested):

use JSON::XS qw(encode_json decode_json);
use File::Slurp qw(read_file write_file);
my %hash;
{
    my $json = encode_json \%hash;
    write_file('dump.json', { binmode => ':raw' }, $json);
}
{
    my $json = read_file('dump.json', { binmode => ':raw' });
    %hash = %{ decode_json $json };
}

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use YAML::XS qw(Load Dump);
use File::Slurp qw(read_file write_file);
my %hash;
{
    my $yaml = Dump \%hash;
    write_file('dump.yml', { binmode => ':raw' }, $yaml);
}
{
    my $yaml = read_file('dump.yml', { binmode => ':raw' });
    %hash = %{ Load $yaml };
}

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The next step up from here is object persistence.

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Also read: Serializers for Perl: when to use what